Tor onion service INTRODUCE2 invalid-MAC cells permanently grow service replay cache

A remote client can send well-formed v3 `INTRODUCE1` cells whose encrypted section has an invalid MAC but a unique byte pattern. The introduction point parses and forwards these cells to the onion service as `INTRODUCE2`. On the service side, `hs_cell_parse_introduce2()` inserts the …

if (replaycache_add_test_and_elapsed(data->replay_cache, encrypted_section,
                                     encrypted_section_len, &elapsed)) {
  ...
  goto done;
}

...
intro_keys = get_introduce2_keys_and_verify_mac(data, encrypted_section, …